1. Field of the Invention
The present invention is directed to an optical fiber switching system for laser welding, and more particularly to such a system for selectively distributing a laser beam from a source of laser to one of a plurality of welding stations for effecting a laser welding thereat.
2. Description of the Prior Art
In order to effect a laser welding at different work stations by a common laser beam generated from a laser source, it has been proposed to distribute the laser beam selectively through a plurality of optical fibers leading to the individual work stations. One prior art system is shown in FIG. 25, which has a switching device 250 comprising a plurality of mirror units 251 arranged in a row on the side of a laser source 200 and connected to different work stations WS respectively through corresponding optical fibers 210. Each of the mirror units 251 includes a mirror 252 which is controlled to move between an operative position for reflecting a laser beam LB from the laser source 200 to the corresponding optical fiber 210 and an inoperative position for passing the laser beam LB to the next mirror unit 251. Another prior art system is shown in FIG. 26, which includes a switching device or distributor 260 with a plurality of output terminals 261 which are connected to individual work stations WS through a corresponding number of optical fibers 210. The distributor 260 is mounted on the side of the laser source 200 and includes a rotor 262 with a mirror which is driven by a motor to reflect the laser beam LB selectively to one of the output terminals 262. In these system, however, the switching device adds an extra volume or bulk to the laser source, thereby making it space-consuming and less convenient for installation within a limited space. Also because of that the switching devices are mounted on the side of the laser source, the optical fibers are all required to be extended from the installation site of the laser source over an entire distance to the individual work stations, necessitating unduly long total length for the optical fibers. Further, the former system of FIG. 25 is expected to operate only at a slow switching rates, such as less than 10 MHz and it is difficult to obtain a higher switching rate operation due to the fact that the mirror 252 must move through a rather great distance between the operative and inoperative positions. While on the other hand, the latter system of FIG. 26 is capable of a high switching rate operation, as high as 40 MHz by controlling the motor. Nevertheless, the system is found to inherently suffer from different switching time between switching the laser beam from one of the output terminals to the adjacent terminal and to a remote terminal, thereby failing to effecting switching at a constant rate to all of the optical fibers. To solve the above problems while retaining a high switching operation, it is assumed to utilize a switching device which is connected to the laser source through a single optical fiber and to the individual work stations through a corresponding number of optical fibers so that the switching device can be mounted separated away and independently from the laser source. The switching device may comprise a relay with an armature having two positions which is connected to move the optical fibers extending from the laser source between two position for selectively connecting it to one of the optical fibers leading to the work stations. Such a switching device, by itself, is know in the art of a fiber optical communication system as, for example, disclosed in U.S. Pat. Nos. 4,337,995, 4,452,507, and 4,610,504. However, since the switching device for the fiber optical communication deals only with a light of very small energy, such switching device is not directly transferable to the optical fiber switching system for laser welding where the light energy is so great that heat protection becomes of major concern for safely switching the laser beam to a selected one of the work stations through the corresponding optical fibers.